Python-сообщество

 from PyQt4 import  QtCore,QtGui
import sys
class Test(QtGui.QMainWindow):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.setWindowTitle('...test')
        self.show()
class Begin(QtGui.QMainWindow):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.setWindowTitle('BEGIN.....')
        self.show()
class MyWindow(QtGui.QWidget):
    def __init__(self):
        super(MyWindow, self).__init__()
        btn1=QtGui.QPushButton(self, text='test')
        btn1.clicked.connect(self.test)
        btn2=QtGui.QPushButton(self, text='begin')
        btn2.clicked.connect(self.begin)
        self.grid = QtGui.QGridLayout()
        self.setLayout(self.grid)
        self.grid.addWidget(btn1,0,0)
        self.grid.addWidget(btn2,0,1)
        self.show()
    def test(self):
        self.a = Test()
    def begin(self):
        self.a = Begin()
if __name__ == '__main__':
    app1 = QtGui.QApplication(sys.argv)
    window = MyWindow()
    sys.exit(app1.exec())

 from PyQt5.QtWidgets import \
    (QWidget, QPushButton, QApplication, QLabel, QComboBox, QLineEdit, QGridLayout, QMessageBox, QListWidget)
from PyQt5.QtCore import Qt
class one(QWidget):
    def __init__(self):
        super().__init__()
        # ...
        self.start()
    def start(self):
        self.layout = QGridLayout()
        self.setLayout(self.layout)
        self.setGeometry(100, 100, 600, 500)
        # ...
        self.show()
class two(QWidget):
    def __init__(self):
        super().__init__()
        # ...
        self.start()
    def start(self):
        self.layout = QGridLayout()
        self.setLayout(self.layout)
        self.setGeometry(100, 100, 600, 500)
        # ...
        self.show()
def main():
    app = QApplication(sys.argv)
    def start1():
        s1 = one()
    def start2():
        s2 = two()
    root = QWidget()
    root.layout = QGridLayout()
    root.setLayout(root.layout)
    root.setGeometry(100, 100, 600, 500)
    # ...
    root.butt = QPushButton(text='start 1')
    root.butt.clicked.connect(start1)
    root.layout.addWidget(root.butt, 1, 1)
    root.butt = QPushButton(text='start 2')
    root.butt.clicked.connect(start2)
    root.layout.addWidget(root.butt, 2, 1)
    root.show()
    sys.exit(app.exec_())
if __name__ == "__main__":
    main()